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Galena Background
Galena is relatively abundant mineral that has a gray, streaked appearance and metallic luster. The ease in melting and casting the lead component of galena ore resulted in its historic use for containers and piping. Galena has a specific gravity of 7.5, resulting in a heavy feel, and it has a hardness of 2.75 on Mohs hardness scale, meaning that it can be scratched easily with a penny.
Refinement Methods
Galena ore must be refined to produce pure lead. The lead portion of galena ore begins to melt within the temperature range of a very hot campfire, at approximately 620 degrees Fahrenheit. For this reason, lead balls and eventually lead bullets were made by melting galena ore and pouring the molten lead into casts. The two main modern methods for refinement are roasting and smelting, as well as chlorination and electrolysis.
Preparation for Roasting and Smelting
The roasting and smelting refinement has several specific steps. The galena ore must be processed before the roasting and smelting. First, mined galena ore is crushed into sugar-like powder, and then it is added to a large tank with water and a small amount of pine oil. The tank is agitated vigorously, and air is diffused throughout the tank, causing sulfide particles to float to the top. The remaining fluid in the tank is then filtered, and this ore concentrate will contain about 60 percent lead.
Roasting and Smelting
The ore concentrate is mixed with additives is spread across a moving grate where air that has been heated to about 2,500 degrees Fahrenheit passes through the grate and roasts the ore concentrate. The roasted lead concentrate is then blasted with hot air, and the molten lead is poured off into casts or other containers where it is kept above 700 degrees Fahrenheit for several days to purify the lead further. Addition of chlorine gas lowers the melting point by approximately 200 degrees Fahrenheit, depending on the accessory minerals in the galena ore.